Published: August 21, 2012

What are the odds of survival for people whose hearts stop -- not in a hospital, but out in the world -- and who receive cardiopulmonary resuscitation, at least long enough to get to a hospital and then to be discharged from it?

Most of us have watched too much television -- one minute the heroic medical worker pumps the victim's chest and grabs the defibrillator paddles and yells ''Clear!,'' and in the next scene the victim is sitting up, chatting with detectives -- to have any realistic idea.

It's not an easy question to answer anyway, depending as it does on whether someone sees the patient collapse or whether it happens unobserved, on how long it takes before CPR starts and then how long before skilled medical personnel can begin the rest of the advanced cardiac drill (drugs, defibrillation, airways). The particular type of cardiac arrhythmia involved matters; so do other illnesses the patient may have, and how frail she is.

But as a ballpark figure, let's say that maintaining a heart rate by chest compression until the cavalry arrives succeeds no more than 20 percent of the time. That estimate comes from Dr. David John, an emergency room doctor in Massachusetts and Connecticut for 20 years and the former geriatrics chairman of the American College of Emergency Physicians. Some studies put the proportion much lower, some higher.

One study following about 2,600 out-of-hospital cardiac arrests over four and a half years in Oakland County, Mich., found that patients in their 40s and 50s had the highest rate of successful resuscitation: 10 percent. The statistics got only slightly worse with each decade: 8.1 percent successful resuscitation for patients in their 60s, 7.1 percent in their 70s. After 80, though, only 3.3 percent survived to hospital discharge.

In King County, Wash., where a surveillance system tracks every out-of-hospital cardiac arrest, University of Washington researchers focused on the very elderly and found that 9.4 percent of octogenarians and 4.4 percent of nonagenarians survived after CPR, compared with 19.4 percent of younger patients. All three groups did much better if they had the heart arrhythmias known as ventricular fibrillation or ventricular tachycardia, but those occurred more commonly in younger people, so survival among those in their 80s and 90s improved to only 24 percent and 17 percent, respectively. (This study included CPR done by bystanders, paramedics or both, which might have affected the results.)

The authors of these and other studies take pains to say that age alone is not a basis for doing CPR or withholding it. You could be the diabetic 53-year-old who dies or the (rarer) robust 83-year-old with the ''right'' heart arrhythmia who pulls through. Moreover, the wider distribution of automated external defibrillators in airports and malls and the ubiquity of cellphones -- both can mean less time between collapse and help -- may have improved results since these studies were done.

But since older people are much more likely to have other diseases and health problems -- and since merely getting discharged from the hospital doesn't tell us much about what your subsequent life is like (can you speak? walk? remember?) or where you live it or for how long -- I think CPR raises a dilemma for older adults.

CPR doesn't work very often, and it works slightly less often on those beyond 70 and considerably less often at more advanced ages. Do you agree to it, for yourself or your relative? Call 911 and let the emergency technicians, the people most commonly performing CPR and defibrillation these days, do their best? Or do you say no?

It's such a deeply personal decision that it's not surprising that even those on the front lines of emergency medicine aren't sure of the proper answer.

PHOTO: LIFESAVER? Cardiopulmonary resuscitation doesn't work very often, and it's even less effective in people of advanced age. (PHOTOGRAPH BY JUSTIN SULLIVAN/GETTY IMAGES)